October 2013 - Haskell-Cafe

Interfacing real-time stocks data API
by Miro Karpis 09 Oct '13

09 Oct '13

Please, did/does anybody tried to interface with Haskell some real-time stocks data API? If yes, please which one? So far I came down to ActveTick,... thanks, m.

6 5

Case studies, step two
by Mike Meyer 09 Oct '13

09 Oct '13

I want to thank everyone who provided pointers for the last question about this. They were a big help. We're now trying to narrow things down a bit. If you have either converted part of a business project from a language like ruby or python to Haskell, or have a business project that integrates Haskell with such a language and are willing to take a short survey about it, could you get back to me? Thanks

1 0

Fwd: [Haskell-beginners] RankNTypes + ConstraintKinds to use Either as a "union"
by Thiago Negri 09 Oct '13

09 Oct '13

(from thread: http://www.haskell.org/pipermail/beginners/2013-October/012703.html) Why type inference can't resolve this code? > {-# LANGUAGE RankNTypes, ConstraintKinds #-} > > bar :: (Num a, Num b) => (forall c. Num c => c -> c) -> Either a b -> Either a b > bar f (Left a) = Left (f a) > bar f (Right b) = Right (f b) > > bar' = bar (+ 2) -- This compiles ok > > foo :: (tc a, tc b) => (forall c. tc c => c -> c) -> Either a b -> Either a b > foo f (Left a) = Left (f a) > foo f (Right b) = Right (f b) > > foo' = foo (+ 2) -- This doesn't compile because foo' does not typecheck > > -- Kim-Ee pointed out that this works: > type F tc a b = (tc a, tc b) => (forall c. tc c => c -> c) -> Either a b -> Either a b > foo' = (foo :: F Num a b) (+2)

1 0

FP relates events in NYC
by Dan Frumib 09 Oct '13

09 Oct '13

Hi folks, I will be visiting New York at the end of the October and I would like to catch some cool Haskell events if possible. I'll be staying in the city from 29th of October to the 10th of November and I would like to plan my trip ahead. I am looking for anything nerdy: talks, seminars, user groups, etc Thanks - Dan

1 0

Re: [Haskell-cafe] Interfacing real-time stocks data API
by Alexey Uimanov 09 Oct '13

09 Oct '13

Yes, the trading system, or code generator. It depends on what would be easier to implement. But firstly I need a simulator and history data crawler what I am working on. 2013/10/9 Miro Karpis <miroslav.karpis(a)gmail.com> > Hi Alexey, > thank you for response. You wrote that you are developing package for > testing trading systems. Are you planning to also build a trading system? > > Regards, > Miro > > > On Wed, Oct 9, 2013 at 10:28 AM, Alexey Uimanov <s9gf4ult(a)gmail.com>wrote: > >> I did not find such a library, but I am interested in Haskell trading >> automation too. >> >> BTW, I am developing package for testing trading systems, it can just >> download historical data from some free russian stock services for now. >> >> https://github.com/s9gf4ult/hadan >> >> If you interested we could join forces. >> >> >> 2013/10/9 Miro Karpis <miroslav.karpis(a)gmail.com> >> >>> Please, did/does anybody tried to interface with Haskell some real-time >>> stocks data API? If yes, please which one? So far I came down to >>> ActveTick,... >>> >>> thanks, >>> m. >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

1 0

ANN: hsqml-0.2.0.0
by Robin KAY 08 Oct '13

08 Oct '13

Dear All, I would like to announce version 0.2.0.0 of the HsQML graphics library. HsQML provides a Haskell binding to the Qt Quick framework. It allows you to write graphical applications where the front-end is written in Qt Quick's QML language (incorporating JavaScript) and the back-end is written in Haskell. The two layers are coupled together via a facility to define custom JavaScript objects through which QML code can call into Haskell and vice versa. HsQML requires an installation of Qt 4.7 or 4.8 (including QtDeclarative) present on your path. This release introduces several new features, including support for firing QML signals from Haskell code and MacOS support. A number of bugs have also been resolved. For more information, please see my web site [1] and the Hackage page [2]. The hsqml-morris demo application [3], which implements the game of Nine Men's Morris against an AI opponent, has also been updated to 0.2.0.0. It now uses QML signals to run the game's AI processing outside of the event loop so as to maintain a responsive UI. My goals for the next release are to work on writing a proper user manual and to migrate the library over to work with Qt 5.x. [1] http://www.gekkou.co.uk/software/hsqml [2] http://hackage.haskell.org/package/hsqml-0.2.0.0 [3] http://hackage.haskell.org/package/hsqml-morris-0.2.0.0 Regards, -- Robin KAY

1 0

ANN: E-book version of the Typeclassopedia
by Erlend Hamberg 08 Oct '13

08 Oct '13

While re-reading Brent Yorgey's Excellent Typeclassopedia I converted it to Pandoc Markdown in order to be able to create an EPUB version. Having a “real” e-book meant that I could comfortably read it on my e-book reader and highlight text and take notes while reading. I also fixed some minor issues while reading it. (These fixes were of course backported to the official Typeclassopedia version on the Haskell Wiki.) The EPUB file can be downloaded from Github: https://github.com/ehamberg/typeclassopedia-md/releases The Markdown source is also available in that repo and you can of course use Pandoc to convert the Markdown file to all the other output formats Pandoc supports. By using a program like Calibre, the EPUB file can be converted to other e-book formats such as the Kindle format. I hope people find this useful. :-) -- Erlend Hamberg ehamberg(a)gmail.com

5 4

POSA
by Kazu Yamamoto 07 Oct '13

07 Oct '13

Hi all, Michael Snoyman, Andreas Voellmy and I are invited to write an article about Warp to "The Performance of Open Source Applications": http://aosabook.org/en/index.html It is now open to the public including our article. http://aosabook.org/en/posa/warp.html Enjoy! --Kazu

1 0

A question regarding reading CPP definitions from a C header
by Ömer Sinan Ağacan 07 Oct '13

07 Oct '13

Hi all, Let's say I want to #include a C header file in my Haskell library just to read some macro definitions. The C header file also contains some C code. Is there a way to load only macro definitions and not C code in #include declarations in Haskell? What I'm trying to do is I'm linking my library against this C library but I want to support different versions of this C library, so I want to read it's version from one of it's header files. The problem is the header file contains some C code and makes my Haskell source code mixed with C source before compilation. Any suggestions would be appreciated, Thanks, --- Ömer Sinan Ağacan http://osa1.net

3 4

Lenses that work with Arrows
by Tom Ellis 07 Oct '13

07 Oct '13

Dear all, I introduce a very simple extension to the Lens datatype from Control.Lens that allows it to work with Arrows: https://gist.github.com/tomjaguarpaw/6865080 I would particularly like to discuss this with authors of Control.Lens to see if such an idea is suitable for inclusion in their library. I have also started a Reddit discussion here: http://www.reddit.com/r/haskell/comments/1nwetz/lenses_that_work_with_arrow… Tom

2 3